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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

NUNATAK AND CASCADING GLACIERS                        139
the glacier. Off shore from this point, in 1909, there was a submerged reef, extending three-quarters of a mile from shore, sufficiently shallow for the stranding of large icebergs. Soundings made in 1910 show that this is probably part of the morainic deposit made during a halt in the glacial recession. A halt is suggested by the comparison between the position of Nunatak Glacier in 1895, as indicated by the Boundary Commission map, and its known position in 1899. Upon this evidence the rate of recession between 1895 and 1899 was about 1150 feet a year, or half as fast again as between 1899 and 1909. If recession between 1891 and 1895 was as fast even as the rate between 1899 and 1909 (860 feet per year) it would carry the tidal arm of the glacier out far enough to have led Uussell, from his distant point of view at Cape Enchantment, to have inferred that the land tongue and the extended tidal end of Nunatak Glacier actually coalesced. It is to be remembered, however, that Russell did not specifically state that the nunatak was actually surrounded in 1891, though the name "Nunatak," and the statement that it "rises through" the glacier "like an island/' warrant this interpretation of his (description. The rate of recession may have been even more rapid between 1891 and 1895, for the rate from 1895 to 1899 was apparently one and a half times as fast as the rate from 1899 to 1909, perhaps partly as a result of the change in exposure of the glacier front, from southwest to northwest, with the bending of the fiord, and partly of the retreat of the glacier to a position in a narrower fiord with the high nunatak rising south of the 1899 to 1909 ice front, whereas at earlier stages the southern side of the broader glacier rested against low ground which separates the fiord from the southern mountain -wall.
Our observations on the tidal distributary of Nunatak Glacier corroborate the con-€lusion reached from our observations on the land distributary that up to 1909 there was no response in this glacier from the effect of the earthquake shaking of 1899. Nunatak Glacier had undergone steady and extensive recession during the period of observation (PI. LXIX). In this respect it contrasts with the two other tidal glaciers of Yaku-tat Bay, the Turner and Hubbard, both of which give indication of minor fluctuations in then- ice fronts. These two glaciers have either maintained their position or have actually advanced, as has the other large glacier, the Hidden. We felt after our observations in 1909 that it could hardly be believed that in this region, where so many glaciers have advanced under the influence of the 1899 earthquakes, a large glacier like the Nunatak would fail to ultimately respond. We therefore anticipated that before many years the period of recession, so long and effectively in progress, would be brought to an end and be replaced by a sudden forward movement.
Advance of the Tidal Distributary in 1910. The junior author found that between July 24, 1909, and June 17, 1910, the retreat of the tidal arm of Nunatak Glacier had ceased and an advance begun. Our resurvey of the ice front plotted accurately in 1910 on a plane table map made a little less than eleven months before (Map 4), proved the advance to have varied in different parts of the ice front, the advance of the north side of the glacier being 1000 feet, the south side 350 to 400 feet, and the middle of the glacier 700 feet. The 1910 ice front is shown with that of 1909 on Plate LXX. Both margins of the glacier were seen to have extended northwestward down the fiord and the advance of the middle was shown by the lengthening of the medial moraines.
This is well shown in PI. LXX where the photographs in 1909 and 1910 show the advance on both the left (north side of fiord) and on the right margin, as well as an